The present invention relates to the art of medical diagnostic imaging. It finds particular application in conjunction with combined computed tomography (CT) and positron emission tomography (PET) scanners and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also applicable to multi-headed single photon emission computed tomography (SPECT) scanners as well as other combined diagnostic modes.
Diagnostic nuclear imaging is used to study a radionuclide distribution in a subject. Typically, one or more radiopharmaceuticals or radioisotopes are injected into a subject. The radiopharmaceuticals are commonly injected into the subject""s bloodstream for imaging the circulatory system or for imaging specific organs, which absorb the injected radiopharmaceuticals. Scintillation crystal camera detector heads are placed adjacent to a surface of the subject to monitor and record emitted radiation. Typically, the detector heads are rotated or indexed around the subject in order to monitor the emitted radiation from a plurality of directions. The detected radiation data is then reconstructed into a three-dimensional image representation of the radiopharmaceutical distribution within the subject.
One of the problems with both PET and SPECT imaging techniques is that photon absorption and scatter by portions of the subject or subject support between the emitting radionuclide and the detector heads distort the resultant image. In order to obtain more accurate SPECT and PET radiation attenuation measurements, a direct transmission radiation measurement is made using transmission computed tomography techniques. In the past, transmission radiation data was commonly acquired by placing a radioactive isotope line or point source opposite to a detector head, enabling the detector head to collect transmission data concurrently with the other two detector heads collecting emission data. This transmission data is then reconstructed into an image representation using conventional tomography algorithms. From this data, regional radiation attenuation properties of the subject, which are derived from the transmission computer tomography images, are used to correct or compensate for radiation attenuation in the emission data.
One PET scanning technique involves the injection of a radioisotope, which is selectively absorbed by tumors or other tissues of interest. The resulting PET images provide an accurate depiction of a location of the tumors in space. However, because only the radioactive isotope is imaged, the PET images provide no correlation between the image and the surrounding tissue. In order to coordinate the tumors with location within the patient, the same region of the subject is scanned with both the PET scanner and a computed tomography (CT) scanner. In the past, the PET and CT scanners were permanently mounted in a displaced relationship to each other. A patient was moved from one apparatus to the next. However, due to potential patient movement and/or repositioning between the CT scanner and the nuclear camera, this technique provided uncertainty in the alignment of the PET and CT images.
To eliminate the alignment problems associated with physically displaced imaging systems, it would be advantageous to mount the CT and nuclear imaging systems to a common gantry. One prior art system includes a two-headed nuclear system and a low power CT system mounted back to back within a single housing with a common patient support. The CT scanner includes a single row of CT or x-ray detectors and a low power x-ray tube which are axially displaced from the nuclear camera heads. The region of. interest of the subject was shifted to the CT scanning region before or after the PET scan to acquire anatomical mapping data. Due to the single row of CT detectors, the prior art system is limited to acquiring a ten millimeter slice of reconstructed data. Therefore, the system is required to make many scans in order to provide enough slices of reconstructed data for significant volume coverage. Additional scans require added data acquisition and processing delays.
In addition, the prior art system is rather slow, requiring approximately eight minutes to acquire one slice of transmission data. Obtaining a volume image of the region of interest would be even longerxe2x80x94on the order of 25 minutes. Further, the prior art system is not amenable to fluoroscopy and radiography applications during the nuclear study.
The present invention contemplates a new and improved combined diagnostic imaging system which overcomes the above-referenced problems and others.
In accordance with one aspect of the present invention, a diagnostic imaging system includes a stationary gantry, which defines a subject receiving aperture, and a source of penetrating radiation rotatably mounted on the gantry which transmits transmission radiation through a subject disposed in a subject receiving aperture. The radiation source is mounted for rotation around the stationary gantry subject receiving aperture. A two-dimensional flat panel radiation detector detects radiation transmitted by the source after passage of the radiation through the subject in the subject receiving aperture. At least one nuclear detector head is mounted for rotation around the subject receiving aperture. The detector head detects emission radiation emitted by a radiopharmaceutical injected into the subject. At least one reconstruction processor reconstructs transmission radiation received by the two-dimensional flat panel radiation detector and emission radiation received by the nuclear detector head into volumetric image representations. A fusion processor combines the transmission and emission volumetric image representations together.
In accordance with a more limited aspect of the present invention, the source, the flat panel detector, and the at least one nuclear detector head are mounted to a common rotating gantry for rotation around the subject in a common plane of rotation.
In accordance with another aspect of the present invention, a diagnostic imaging system includes a rotating gantry, which defines a subject receiving aperture. A source of penetrating radiation and a two-dimensional flat panel detector generate a computed tomographic image representation of a subject disposed within the subject receiving aperture. A plurality of nuclear detector heads are rotatably mounted to the gantry. Each detector head has a radiation receiving face and a radiation shielding means for selectively restricting and permitting radiation to strike the radiation receiving face. A method of diagnostic imaging includes shielding the plurality of nuclear detector heads from radiation generated by the source of penetrating radiation. Radiation is transmitted from the radiation source through the subject and toward the corresponding two-dimensional flat panel detector positioned across the subject receiving aperture. The transmitted radiation is reconstructed into a volumetric image representation. A radiopharmaceutical is injected into the subject disposed within the subject receiving aperture. The radiation shielding means are positioned such that radiation emitted by the radiopharmaceutical is receivable by the radiation receiving face. Radiation emitted by the radiopharmaceutical is detected and reconstructed into an emission image representation. The reconstructed volumetric and emission image representations are combined into a combined image representation.
In accordance with a more limited aspect of the present invention, the steps of transmitting radiation from the radiation source and reconstructing the transmitted radiation include laterally shifting the two-dimensional flat panel detector and indexing the source of penetrating radiation through an angle of at least 180xc2x0 about the subject receiving aperture.
In accordance with another aspect of the present invention, a diagnostic imaging system includes a first gantry, which defines a subject receiving region, and a plurality of nuclear detector heads mounted to the first gantry around the subject receiving region. The detector heads detect emission radiation emitted by a radiopharmaceutical injected into the subject. A source of penetrating radiation is rotatably mounted to one of the first gantry and a second gantry. The source of penetrating radiation transmits transmission radiation through a subject disposed in the subject receiving region. A two-dimensional flat panel radiation detector detects radiation transmitted by the source after passage of the radiation through the subject in the subject receiving region. At least one reconstruction processor reconstructs transmission radiation received by the two-dimensional flat panel radiation detector and emission radiation received by the plurality of nuclear detector heads into volumetric image representations. A fusion processor combines the transmission and emission volumetric image representations together.
In accordance with a more limited aspect of the present invention, the second gantry onto which the source of penetrating radiation and the two-dimensional flat panel radiation detector are mounted is axially offset from the first gantry.
In accordance with a more limited aspect of the present invention, the plurality of nuclear detector heads include at least three pairs of nuclear detector heads spaced opposite each other across the subject receiving aperture for coincidence detection.
In accordance with a more limited aspect of the present invention, a diagnostic imaging system further includes a radiation shielding means connected to each nuclear detector head for shielding the nuclear detector head from high energy radiation originating from the source of penetrating radiation.
In accordance with a more limited aspect of the present invention, a diagnostic imaging system further includes a radiation shielding means connected to each nuclear detector head for shielding the nuclear detector head from transmission radiation originating from the source of penetrating radiation.
One advantage of the present invention is that it facilitates combined CT/PET diagnostic imaging.
Another advantage of the present invention resides in time-efficient full volume three-dimensional CT data acquisition.
Another advantage of the present invention resides in the ability to perform fluoroscopy during a nuclear study.
Another advantage of the present invention resides in the ability to perform radiography during a nuclear study.
Another advantage of the present invention resides in use of a flat panel detector for use in volume data acquisition and anatomical mapping.
Another advantage resides in the ability to interleave CT and nuclear data collection.
Other benefits and advantages of the present invention will become apparent to those skilled in the art upon a reading and understanding of the preferred embodiments.